Ultraviolet treatment is used for disinfection and sterilization in water supply and sewerage systems (see JP, P2004-223502A).
Ultraviolet lamps are used as the ultraviolet light sources of ultraviolet irradiation apparatuses, and are lit up by using the high-frequency discharge. When the frequency of the high-frequency discharge in an ultraviolet irradiation apparatus is 10 MHz or higher, electric field is dominant in radio-wave leakage from the ultraviolet lamp and the feeder wires in the ultraviolet irradiation apparatus. In this case, it is possible to prevent such radio-wave leakage almost completely by simply shielding the ultraviolet lamp and the feeder wires in the ultraviolet irradiation apparatus with metal. However, in a case where the ultraviolet lamps are lit up by using high-frequency discharge with frequencies of 10 kHz to 10 MHz, inclusive, the magnetic field may leak from the ultraviolet lamp and the feeder wires in the ultraviolet irradiation apparatus, and the magnetic field thus leaked out of the ultraviolet irradiation apparatus may possibly lead to malfunctions of other apparatuses.